Transmission level regulation



July 23, l929 R. K. POTTER 1,721,574

TRANSMI SS ION LEVEL REGULAT ION -Filed Nov. 20, 1925 INVENTR 1735112257' Patented July 23, 1929. i

UNITED STATES PATENT OFFICE.

RALPH K. POTTER, OF NEW YORK, N` Y., ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TRANSMISSION LEVEL REGULATION.

Application lod November 20, 1925.

This invention relates to radio signaling systems` and particularly to means for regulating the transmission level ot a two-way system in order to render the overall equiva- 5 lent ot the system substantially constant.

In radio signaling systemsr` it is desirable to maintain a substantially tixed ratio between the signal strength and noise strength throughout the system so that at the receiv- 10 ing end the signal will be sufficiently stronger than the noise, to render the signal readily selectable. This ratio may be maintained constant by controlling the transmitter out-put at the sending station. It the attenuation is high, it will require a stronger output to maintain the required signal to noise ratio. It the attenuation diminishes, a smaller amount of energy need be transmitted to maintain the required signal to noise ratio.

One ot the objects of this invention is to control the transmitter output by means of a control signal sont out from the receiving station, which control signal will be subjected to the same. degree of attenuation as the communication. wave which is being t-ransmif'ted in the opposite direction.

Other objects oit this invention will be apparent trom the following description `when read in connection with the attached drawing. oit which Figures 1 and Q represent two stations A and B. ot a system o communication` each station preferably employing the same type of circuit, which circuit shows schematically one Ytorni of the invention.

ln Fig. 1. which represents station A, the line L1 serves to connect'. the radio terminal circuit shown in the figure with a distant station or subscriber. This line is connected in a well-known manner with certain ot the windings oit the hybrid coil 1 which has also connected therewith an artificial line 2 serving to balance the real line LV Also connected with the hybrid coil is the transmit-ting branch circuit 3, by means of which the connnunication signals are impressed upon the transmitting` apparatus ot the radio station. This circuit', is connected by the transformer 4; with the `rramilulator Ml Serial No. 70,405.

which may be of any well-known type, but preferably is of that type in which the carrier current is suppressed. This modulating circuit has connected therewith a. source of carrier oscillations 5, which oscillations are inodulated in the device BL by the incom- 5 ing` communication currents. The output :side o'l the modulator is connected by the transformer 6 with a band filter 7, which is preferably ot the type adapted to suppress one ot the bands resulting from modulation and to transmit the other. This band filter is connected with a regulator 8, which in turn is connected by the transformer 9 With the power amplitier 10, and this is connected with the antenna T1 from which. Waves will 65 be radiated to a distant station such as B shown in Fig. 2, where they Will be received by the receiving antenna R2. The oscillator 5 ot Fig. 1 is also connected with the input side ot another modulator, M2, to Which is connected an oscillator 11, producing a control signal intended to modulate the oscillations produced by 5. These carrier fre-- qucncy oscillations as modulated by the control signal are transmitted through the 7 filter 12 and, when regulated as to amplitude by the regulator 13, will be impressed upon the power amplifier 10 and transmitted to the distant station B of Fig. 2 for the purpose o't controlling transmission l'rom that station to station A shown in Fig. 1. The. manner in which this result is attained will loe described later.

The receiving branch of station A comprises a receiving antenna RL which is coupled by the transformer 15 to the filter 16, which has a two Jtold function, one to select the received communication band and impress it upon the circuit of the detector 17, and the other to separate out the control signal band produced atthe distant station B by the circuit containing' the modulator M2, and transmitted therefrom for the purpose of controlling the amplitude of the communication signal sent from the antenna T1 95 to the said distant station. This control signaling band passes into the branch circuit 19d 'with 'which connected a rectifier con- Cil sistinp; ot the tubes 19 and 20, which serves to determine the amplitude ot' the communication side band that will be passed by the regulator 8 and impressed upon the powerampliier 10. The comn'iunication wave is impressed upon the detector 17 and the resultant current is impressed upon the level control circuit comprising' the tubes 21 and 22. The output side ot the tube 21 is connected with the amplilier 3. The tube 22 is connected witlithe input circuit ot theregulator 13 and thus etl'ects a control o't' the amplitude ol the control signal sont out froml the modulator M2. rlhe output side of the amplilier 23 is connected with the line Ll through the hybrid coil 1.

The manner in which the circuit works will perhaps, be best umilerstood it we consider tirst how a communication signal is transmitted from Station A to station B, and is received at station B and translated by the receiving1 branch ol that station, which is similar to the receiving branch of station A. Let it be assumed that a connnunication signal, such as a speech band, is transmitted over the line L, from apparatus connected therewith, and is received at theradio terminal station A for transmission to a subscriber connected with the line Ll which connects with the distant-radio station B. rlhe speech band will pass into the circuit 3 and be impressed by the transformer 4l upon the input side of the y modulator M1, wherein it serves to modulate the carrier oscillations produced by the source 5,y and the two resultant bands will be impressed by the transformer V6 upon the band filter 7. One ot' the bands, as, tor eX- ainple, the upper side band, will be selected and transmitted through the tilter, and the other band will be suppressed. The selected band will pass through the regulator 8, which is normally adjusted to produce a predetermined amplitude. The resultant wave when lgiven the required degree ot amplilication by the `power amplifier 10, will be radiated by the antenna T, Vto the distant radio station B. The received band will be impressed by the receiving antenna R2 upon the receiving circuit,rand after being passed by the filter 16, will be impressed upon the detector 17. This detected signal then passes through the tube 21 and when amT phil-ed by the tube 23', will be impressed upon the line L2 tortransmission tothe dis- CTL tant station. The transmission of a coinmunication signal from station B to station A is likewise etl'ected in the manner described above.

lVhile a communication wave is passing from station A to station B, control signal `waves are being` sent from both stations, but

we need be concerned only with that sent from station B to station A, because this wave controls the level ot the communication wave trom A to B. At station B there is created a control signal band represented by the modulation by M2 ot' the carrier oscillations from the source by a control signal from the source 11. This high irequency control signal passes through the iilter 12 and the regulator 13', and when ampliiied by the power amplifier will be transmitted to the receiving' antenna Pt, of station A, from which station the connnunication signal is then being` transmitted to he dista-nt station B. It is important that the frequency ot the control signal produced by the generators 11 and 11 shall lie just outside the range of commim'ication frequencies, as, ttor exannple, outside the range ot vo-ice frequencies so thatthe iilters 1G and 1G may separate the control signal and the communication signal and send cach into its proper paths. The control signal received by the antenna B, of station A will be impressed upon the filter 16, and will be in turn impressed upon the circuit 18. The tube 19 rectilies the received control signal, that is to say, the carrier frequency modulated by the control frequency from the source 11. The amplitude ot the rectified voltage will, oli. course, depend upon the amplitude ol' the control signal which may vary trom time to time, depending upon its attenuation during the course of its transmission from the antenna T2 to the antenna R1. Since this rectified voltage is impressed upon the grid of the tube 20, the plate voltage of the regulator 8 may be varied and amplitude of the communication wave may be proportioned to meet changing conditions in its path o1 transmission.

ln practice, the attendant at station B observes the level oit the communication signal incoming trom station A and adjusts in the t'ollowingl manner the amplitude ot the control signal sent out trom station B to station A. By manipulating the potentiometer he varies the grrid potential oit 'the tubes 21 and 22. The variation ot the grid potential ot tube 21 varies the amplification of the communication signal that is passing over the receiving branch oit station B to the line LL. Any variation ot the Lgrid potential of tube 22 causes a corresponding variation ot itspla-te current, and since this current flows tln'ough thev resistance 2l connected with the grid circuit ot the. regulator 13 corresponding changes of'potential will be produced on the grid of 13. The amplitude ot' the control signal wave produced by the niodulation ot the carrier oscillations oit source 5 by the control signal ol` source 11 iscontrolled by the grid voltage ot the regulator 13. The attendant at station B will therefore vary the potentiometer 25 in such way as to elt'ect the transmission from station of a control signal of suchv amplitude as to ell'ect the proper adjustment of the regulator S in the communication transnatlSO lll

ting branch at station A. If the attenuation of the connnunication signal between station A and station P is high, the level of the control signal Will accordingly be adjusted by the operator at station B so that when the control signal is received and rectified at station A, the voltage ot the plate circuit of the regulator S will be so increased as to raise the amplitude of the side band passing through the said regulator. In this Way, the side band representing' the communication signal. transmitted from station A, Will be adjusted to meet changes in the attenuating characteristics of its path, which has produced a similar effect upon the control signal transmitted from the distant station l; to the station A shown in Fig. 1.

Now let it be assumed that a communication signal is transmitted from antenna T of station l to the receiving antenna R, at station A. This signal will be passed by the filter 16 to the detector 17, and the detected signal will be impressed upon the level control circuit comprising the tubes 20 and 21. Il the energy level of this received signal is low, which would be determined by the attendant at station A, he would effect an adjustment of the level control by varying the potentiometer and thus Would vary the magnitude of the plate current produced by the tube 2Q. this current flowing through the resistance 2l, which is connected in the input side of the tube 18, controls the grid potential of that tube and thus controls the magnitude of" the control signal transmitted to the distant station. Assuming, as stated, that the level of the received communication signal was low, the adjustment ot the level control device Q5-26 would be made in such Way as to increase the amplitude of the outgoing control signal from the modulator M2. This would be transmitted by the antenna T1 to the distant receiving antenna Rg, and passing there into the branch circuit 18', would serve in the manner similar to that hereinbefore oescribed to increase the amplitude ot' the communication signal wave being transmitted from the antenna T2, Which increase would be effected by the variation of' the plate potential of the regulator 8.

It will therefore be seen that by means of' the arrangements shown in the figures just described, the regulation of' the transmission level of` the connnunication Wave between two stations would be effected from the receiving station by inea-ns of a control signal transmitted from the latter station to the sending station.

For the purpose of simpli'tyi ng the description the invention has been described in connection with a system characterized by carrier suppression and transmission of a single side band, but the invention is not so limited but may be employed in other systems, such The voltaUe produced byl as for example, those in which the carrier and one side band, or the carrier and both side bands are transmitted.

lhile this invention has been' disclosed as embodied ina particular form, it is obvious that it is capable of' embodiment in other and different forms Without departing from the spirit and scope of the appended claims.

lV hat is claimed is:

1. The method of controlling the transmission level in a two-Way radio signaling system Which consists in transmitting a communication signal f'ron'i one vstation to a second station of the said system' and simultaneously transmitting a control signal from the said second station to the said. first station, varying the amplitude of the control signal sent from the second station to the said first station, rcctifying the control signal received by the said first station and controlling the amplitude of the comn'nmication signal transmitted from the first station by the rectified control signal.

2. The method oit controllingr the transmission level in a tivo-Way radio signaling system which consists in transmitting a communication signal from one station to a second station of the said system and simultaneously transmitting a control signal from the said second station to the said first station, varying the magnitude of the control signal in accordance With the magnitude of the communication signal transmitted from' the first station as received at the said second station.

3. ln a transmission level regulating system, the combination with a radio signaling station having transmitting and receiving circuits, of a second station likewise having transmitting and receiving circuits, each transn'iitting circuit of each station having l'neans to efiect the transmission o't a communication signal and also of a control signal, and each receiving circuit having means to control the amplification o't the communication signal transmitted from that station by virtue ot the control signal as received from the said other station.

4. In a transmission level regulating system, the combination with a radio signaling station having transmitting and receiving circuit-s, off a second station likewise having transmitting and receiving circuits, each transmitting circuit of each station having means to effect the transmission of. a communication signal and also of a control signal, and means at each station connecting the said receiving circuit and said transmitting circuit thereat adapted to rectify the control signal received thereat and to control the amplitude of the transmitted communication signal from that station by and in acmission `level in a two-Way high frequency signaling system which consists in transmitting a communication signal from one station to a second station of the said system andv simultaneously transmitting a control signal from the said second station to the first sta-tion, varying the level of the control signal in accordance With the level of the communication signal transmitted from the first station as received at the second station, and changing the level of the communication signal as transmitted from the first station in accordance with changes in level of the said control signal as received at the said first station.

6. The method of controlling the transmission level in a tivo-Way high frequency signaling` system which consists in transmitting a communication Wave from one station of a system' and simultaneously transmitting a control Wave from another station, both of said Waves traversing substantially the same path so as to be influenced to substantially the same degree of factors affecting transmission, varying the level of the said control Wave as transmitted from the said other station according to changes in the level of the communication Wave as received at the said other station, and utilizing thecontrol Wave as thus varied to govern the level of transmission of the said communication Wave from the first mentioned station.

7. The method of 'controlling the transmission level in a two-way high frequency signaling system which consists in transmitting a communication wave from one station of a system and simultaneously transmitting a control Wave from another station, both of said Waves traversing substantially the same path so as to be influenced to substantially the same degree by factors affecting` transmission, determining the vlevel of the communication Wave as received at the said other station, varying the level of the said wave as thus received and simultaneously varying the level of the control wave be- Y ing transmitted from the said other station,

and changing at vthe first mentioned station the vlevel of the communication wave in accordance with changes in the control wave as received at the first mentioned station.

8. fIn a `two-Way signaling system, the combination with a plurality of stations of a transmission medium between them,'each station having a transmitting and receiving branch, means connected With the transmitting branch to produce a high frequency communication Wave, means also connected therewith to produce a high frequency control Wave, t-he frequencies of the said Waves being different, means connected with the receiving branch of each station to select the control waves transmitted' from another station, and means responsive to thesad seleci;

ed control Wave to govern the level of the communication Wave as transmitted.

9. In a two-Way signaling system, the combination With a vplurality of stations of a transmission medium between them, each station .having a transmitting and receiving branch, means connected With the transmitting branch to produce a high frequency communication Wave, means also connected therewith to produce a high frequency control Wave, the 'frequencies of the said Waves being different, means connected With the receiving branch of each station to vary the level ofthe control Wave being transmitted from each station to another station to control the level of the communication Wave being transmitted from the said other station.

10. In a two-Way signaling system, the combination with a plurality of stations of a transmission medium between them, each station having a. transmitting and receiving branch, means connected with the transmitting branch to produce a high frequency communication wave, means also connected therewith to produce a high frequency control Wave. means connected Wit-h the `receiving branch of each station to vary not only the level of the communication Wave received thereat, but also the level of the control wave being transmitted from the said receiving station to the station transmitting the said communication wave.

1l. In a two-Way signaling system, the combination `with a plurality of stations vof a transmission medium between them, each station having a transmitting and receiving branch, Vmeans connected with the transmitting branch to produce a high frequency communication Wave, means also connected therewith to produce a high frequency control Wave, the frequencies of the said Waves being different, means connected with the receiving branch of .each station to separate, Vby filtering, -the received control Wave from the received communication Wave, means to 4detect the communication signal, means to amplify the comn'lunication signal and `means connected with the said amplifying means to vary, at will, the level of the communication -Wave as received at each station and also to simultaneously vary, at Will, the level of the control Wave-being transmitted from the same station.

12. In a two-Way signaling system, the combination with a plurality of stations of a transmission medium connecting them, each station having a transmitting branch comprising a source of high frequency waves, a source of communication signals to modulate 4the said Waves, a source of control signals to modulate the said Waves, means to regulate the said modulated communication Waves, means to insulate the modulated sono trol Waves, and a receiving branch comprising means to separate, loy filtering, the communication Waves and the control Waves, means to detect the communication signal, means to amplify the communication signal, means to detect the control signal, means et'- fectively connecting the latter detector With the means to regulate the communication Waves in the transmitting branch of the same station and means connected with the amplifier of the communication signal to govern the operation of the regulating means of the cont-rol Waves connected Wit-li the transmitting branch of the same station.

In testimony whereof, I have signed my name to this specification this 19th day of N ovember, 1925.

RALPH K. POTTER. 

